An organic solar cell is a device that may directly convert solar energy into electrical energy by applying a photovoltaic effect. A solar cell may be classified into an inorganic solar cell and an organic solar cell depending on a material constituting a thin film. A typical solar cell is manufactured with a p-n junction obtained by doping crystalline silicon (Si), which is an inorganic semiconductor. Electrons and holes generated due to absorption of light diffuse to a p-n junction point, and are accelerated by an electric field and moved to an electrode. Power conversion efficiency of this procedure is defined as a ratio of power given in an external circuit to solar power fed into the solar cell, and reaches up to 24% when measured under the virtual solar irradiation conditions currently standardized. However, since the inorganic solar cell in the related art already has limits in economic feasibility and available materials, an organic semiconductor solar cell, which is easily processed and cheap and has various functionalities is in the spotlight as a long-term alternative energy source.
In the solar cell, it is important to increase the efficiency such that electrical energy as much as possible may be outputted from the solar energy. In order to increase the efficiency of the solar cell, it is also important to generate excitons as much as possible from inside the semiconductor, but it is also important to take out electric charges generated to the outside without being lost. One of the causes that electric charges are lost is that generated electrons and holes are annihilated by means of recombination. As a method of transferring generated electrons or holes to an electrode without being lost, various methods have been suggested, but most of the methods require additional processes, and as a result, manufacturing costs may be increased.